The Development of a Cyclone–Anticyclone Asymmetry within a Growing Baroclinic Wave

Abstract

Abstract This study examines the cyclone–anticyclone asymmetry within idealized baroclinic waves. For this purpose a primitive equation (PE) model and a quasigeostrophic (QG) model are used. The Rossby number appears to be an essential external parameter for the cyclone–anticyclone asymmetry. Consequently, the Rossby number effect on nonlinear baroclinic waves is a central point of this study. First, the baroclinic stability of a vertically antisymmetric dipole jet flow is analyzed. Increasing the Rossby number in the PE model has the effect that the eddies of the fastest growing normal mode are tilted toward the northwest–southeast direction. The increase of this tilt is almost proportional to the Rossby number and arises due to leading-order corrections to the QG model. The nonlinear development of the fastest growing normal mode is simulated for various Rossby numbers. The PE model simulations exhibit the development of strong cyclones and weak anticyclones even when the cyclonic and anticyclonic shear...